#include <stdio.h>

int main() {
    int N;
    scanf("%d", &N); 

    double sum = 0.0;
    int a = 2, b = 1; 

    for (int i = 1; i <= N; i++) {
        sum += (double)a / b;  
        int c = a + b;
        int d = a;
        a = c;
        b = d;
    }

    printf("%.2f\n", sum);
    return 0;
}
